Remember when I joined I was shown the way we dispatched U boats to the sea bottom with this anti-sub killer instead of depth charges.
My first ship[Chichester] had Squid so I never really understood these Hedgehogs as I was Gunnery.
Question for me is:
1. If they exploded on impact why didn't they do so after hitting the sea as they came down heavy and the fuse must have been sensitive?
2.after entering the sea surely they would drop down at a slower speed making it's contact with a sub not too hard[hence my question re.fuse sensitivity on entering the sea.]
3.Why did they not incorporate a depth trigger so they all went off at different depths if no contact made as that may have enveloped the sub in a deadly pattern,they did with depth charges .
Now there is a good reason and answer for these questions that a TAS man can answer it's just I always wondered as they were successful it seems.
Just an old man's curiosity if you can.

I believe (not being TAS) that the thinking behind the impact fuse was that the explosion would not totally scramble the water as a pattern of DCs would, making a rapid follow up attack by another vessel easier to carry out.

That's an intriguing question to me, especially since I've been involved with A/S mortars as well as gunnery.

I've no doubt the Hedgehog "boffins" knew what they were doing when they designed it and this pic of the anmo suggests that the fuze wasn't armed until after a designed distance/depth had been traversed through the water.

What I mean is that there appears to be an impellar on the pointy end of the projojectile - maybe that's an aquadynamic delay arming device?

On the 19th of September at 16.30 whilst engaged on these duties the ASDIC team of MOUNTS BAY made contact in position latitude 36Â°.55 north and longitude 126Â°.06 west, classified as "possible" submarine. Once again the alarm rattlers sounded and with the ships company closed at action stations an attack commenced. A full pattern of 10 depth charges was dropped. On return on the target area no result was observed but contact was regained. A second attack developed using the Hedgehog, an ahead throwing weapon comprising of 24 projectiles containing 32 lbs of torpex explosive based on the mortar principal and fired in quick succession. The 24 spigots on which the projectiles sat were arranged in 6 rows of 4 and offset so the Hedgehog bombs entered the water ahead of the ship in a circle of about 130 feet in diameter. The bombs were armed by an impeller located on the nose which rotated as it passed through the water actuating the percussion fuse allowing the bomb to explode on contact.

On the 19th of September at 16.30 whilst engaged on these duties the ASDIC team of MOUNTS BAY made contact in position latitude 36Â°.55 north and longitude 126Â°.06 west, classified as "possible" submarine. Once again the alarm rattlers sounded and with the ships company closed at action stations an attack commenced. A full pattern of 10 depth charges was dropped. On return on the target area no result was observed but contact was regained. A second attack developed using the Hedgehog, an ahead throwing weapon comprising of 24 projectiles containing 32 lbs of torpex explosive based on the mortar principal and fired in quick succession. The 24 spigots on which the projectiles sat were arranged in 6 rows of 4 and offset so the Hedgehog bombs entered the water ahead of the ship in a circle of about 130 feet in diameter. The bombs were armed by an impeller located on the nose which rotated as it passed through the water actuating the percussion fuse allowing the bomb to explode on contact.

Saw a prog on Sky this morning called 'Treasure Quest', where (instead of looking for treasure) they were looking for lost U Boats from WW2 to assist an UBoat historian in tracking and identifying lost WW2 UBoats.

Showed some footage of this weapon in operation - very effective indeed.

Also showed the remains of a boat found off of Lands End where the pressure hull had been completely ripped open by the use of these bombs. Not a nice demise for the crew !